268 ELECTRICITY OF THE AIR ; LIGHTNING. 



Every sound requires, as you know, a certain time 

 to travel from the place at which it starts, to any 

 distance at which it may be heard. The speed 

 with which sound is sent through the air is about 

 one thousand one hundred and forty-two feet in a 

 second. Light coming from any source on the 

 earth, and, therefore, also from lightning, if it 

 reaches the eye at all, is perceived at the very 

 moment at which it issues. The number of seconds, 

 therefore, that pass between the instant at which 

 the light of the flash reaches the eye, and that at 

 which the sound reaches the ear, multiplied by 

 1142, will give the distance in feet between the 

 place where the observer stood and the spot where 

 the flash occurred. 



Every thunder-cloud may be compared, as I 

 have already mentioned, to a conductor charged 

 with electricity, and insulated by the surrounding 

 air. If an electrised conductor be insulated and sur- 

 rounded with various substances, good conductors 

 and bad, the natural electrical condition of all of 

 them, without exception, will be disturbed, the 

 electricity, like to that of the conductor, will be 

 driven from it, and the unlike drawn towards the 

 conductor. The tension thus given to the elec- 

 tricity, gathered up and struggling against the non- 

 conductor that keeps it back — against the air, — is 

 greater the nearer the conductor is approached by 

 the bodies around it. This sundering, however, 



